Self-limiting wear contact pad slider and method for making the same

ABSTRACT

The present invention provides a non-actuatable, self-limiting wear contact pad slider and method for making the same. A protruding element surrounding the transducer is fabricated using a third etch step so that the protruding element has a height that is greater than or equal to the designed fly height of the aerodynamic lift surface minus the disk roughness.

RELATED PATENT DOCUMENTS

This is a divisional of U.S. Pat. No. 6,714,382, filed on Oct. 13, 2000(SJO0000026 US01), to which Applicant claims priority under 35 U.S.C.§120.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates in general to data storage systems, and moreparticularly to a self-limiting wear contact pad slider and method formaking the same.

2. Description of Related Art

Fixed magnetic disk systems, typically referred to as “hard” diskdrives, are now commonplace as the main non-volatile storage in modempersonal computers, workstations, and portable computers. Such hard diskdrives are now capable of storing gigabyte quantities of digital data,even when implemented in portable computers of the so-called “notebook”class. Many important advances have been made in recent years that haveenabled higher data density and thus larger storage capacities of harddisk drives, and that have also enabled much faster access speeds, bothin the bandwidth of data communicated to and from the hard disk drive,and also in the access time of specified disk sectors. Advances havealso been made that have greatly reduced the size and weight of harddisk drives, particularly as applied to portable computers, have beenmade over recent years. These advances have resulted in the widespreadavailability of ultra-light portable computers, yet having state-of-theart capability and performance.

A head/disk assembly typically comprises one or more commonly drivenmagnetic disks rotatable about a common spindle and cooperating with atleast one head actuator for moving a plurality of transducers radiallyrelative to the disks so as to provide for the reading and/or writing ofdata on selected circular tracks provided on the disks. The magnetictransducer or “head” is suspended in close proximity to a recordingmedium, e.g., a magnetic disk having a plurality of concentric tracks.The transducer is supported by an air bearing slider mounted to aflexible suspension. The suspension, in turn, is attached to apositioning actuator.

During normal operation, relative motion is provided between the headand the recording medium as the actuator dynamically positions the headover a desired track. The relative movement provides an air flow alongthe surface of the slider facing the medium, creating a lifting force.The lifting force is counterbalanced by a predetermined suspension loadso that the slider is supported on a cushion of air. Air flow enters theleading edge of the slider and exits from the trailing end. The headresides toward the trailing end, which tends to fly closer to therecording surface than the leading edge.

The recording medium holds information encoded in the form of magnetictransitions. The information capacity, or areal density, of the mediumis determined by the transducer's ability to sense and writedistinguishable transitions. An important factor affecting areal densityis the distance between the transducer and the recording surface,referred to as the fly height. It is desirable to fly the transducervery close to the medium to enhance transition detection. Some flyheight stability is achieved with proper suspension loading and byshaping the air bearing slider surface (ABS) for desirable aerodynamiccharacteristics.

Another important factor affecting fly height is the slider's resistanceto changing conditions. If the transducer fly height does not stayconstant during changing conditions, data transfer between thetransducer and the recording medium may be adversely affected. Flyheight is further affected by physical characteristics of the slidersuch as the shape of the ABS. Careful rail shaping, for example, willprovide some resistance to changes in air flow.

Hard drive manufacturers are starting to incorporate proximity recordingtype sliders in drives in order to achieve higher storage densities. Theproximity recording slider is designed to maintain a small area near theread-write element in constant contact with the disk, and thus enablingsmaller bit size and ultimately larger storage densities. This approachto increasing storage density puts considerable amount of strain oncontrolling wear at the slider-disk interface, because a slightvariation in contact load and contact area could greatly affect thedrive survivability.

Slider-disk contact results in lubricant depletion and degradation, wearof both surfaces, generation of wear particles, stick-slip, etc. Allthese phenomena affect magnetic performance of the disk drive, e.g.,through jitter, as well as its durability. Nevertheless, as mentionedabove, a contact slider is key for high-density magnetic recording.

As product fly heights are getting closer to the disk to increase arealdensity, the ultimate fly height goal will be to put the element incontact with the disk media, thus reducing the fly height to zero.However in practice, a reliable contact interface is very difficult toachieve due to the wear of the head and disk, resulting in early failurewhen compared to higher fly heights with a cushion of air between them.The reliability problem is exacerbated by manufacturing tolerances whichresults in significant variation in the amount of interference in thecontact interface. Even with a product design point centered nominallyat zero fly height or contact, manufacturing tolerances for both diskroughness and head fly height result in a distribution of interferencesuch that half the interfaces will have negative (i.e., too much)interference and wear out prematurely and the other half will havepositive (i.e., too little) interference and fly with an air separationwhich will cause poor magnetic performance.

U.S. Pat. No. 5,761,003, entitled “Magnetic head slider with crown ABS”,issued Jun. 2, 1998, to Toshiharu Sata, which is assigned to CitizenWatch Co., Ltd., and which is incorporated by reference herein,discloses a magnetic head slider including a crown air-bearing surface(ABS) adapted to be located opposite to a magnetic disk. The ABSincludes a rear pad with a convexly curved upper surface, arranged at acenter of the air-discharging end and longitudinally spaced from theboundary. The rear pad has such a small dimension that a dynamicpressure due to the air introduced onto the ABS is hardly applied to therear pad. However, the slider design is not made to fly in contact withthe disk such that the interference is zero over a wide range ofmanufacturing tolerances.

One slider design that attempts to achieve contact recording isdisclosed in “An Active Slider For Practical Contact Recording”, IEEETransactions On Magnetics, Vol. 26, No. 5, September 1990, pp.2478–2483, by C. E. Yeak-Scranton et at. (herein referred to as “ActiveSlider article”). In the “Active Slider article” active material islaminated into a thin-film head to form an actuatable bender at thetrailing end of the slider. The actuatable area allows the recordinghead to be raised or lower thereby providing contact recording whenneeded, but preventing rapid failure of the interface.

Nevertheless, the design is complex because it requires not onlyadditional processing steps to add the laminated active material, butalso additional circuitry to control and supply the bender drivevoltage.

It can be seen then that there is a need for a simple head design thatcan be made to fly in contact with the disk such that the interferenceis zero over a wide range of manufacturing tolerances.

SUMMARY OF THE INVENTION

To overcome the limitations in the prior art described above, and toovercome other limitations that will become apparent upon reading andunderstanding the present specification, the present invention disclosesa self-limiting wear contact pad slider and method for making the same.

The present invention solves the above-described problems by fabricatinga protruding element surrounding the transducer using a third etch stepso that the protruding element has a height that is greater than orequal to the designed fly height of the aerodynamic lift surface minusthe disk roughness.

A slider in accordance with the principles of the present inventionincludes a support structure having a leading and a trailing edgerelative to the motion of the recording medium and an air bearingstructure positioned on the support structure extending to the trailingedge of the support structure, the air bearing structure having an airbearing surface and a non-actuatable, wearable pad positioned at thetrailing end of the air bearing structure and extending above the airbearing surface, the air bearing surface being formed to provide adesired fly height and the wearable pad having a surface area of lessthan 5% of a total air bearing surface area and a predetermined heightso that wearing of the pad during use produces an interference of zeroat the desired fly height and provides negligible lift to the slider.

Other embodiments of a slider in accordance with the principles of theinvention may include alternative or optional additional aspects. Onesuch aspect of the present invention is that the air bearing surfacefurther comprises at least one aerodynamic lift surface level generatinglift to provide the desired fly height, the non actuatable, wearable padcomprising a last surface level extending above the at least one surfacelevel of the air bearing surface.

Another aspect of the present invention is that the at least one surfacelevel further comprises two surface levels.

Another aspect of the present invention is that the non-actuatable,wearable pad is formed around a magnetic sensor.

Another aspect of the present invention is that the air bearing surfaceis formed using two etch steps and the non-actuatable, wearable pad isformed using a third etch step.

Another aspect of the present invention is that the wearable pad forms afourth surface level to the slider.

Another aspect of the present invention is that the predetermined heightof the non-actuatable, wearable pad is selected to be greater than orequal to the desired fly height minus a disk roughness.

Another aspect of the present invention is that the slider furtherincludes at least one front air bearing pad.

Another aspect of the present invention is that the slider furtherincludes side rails extending along sides of the support structure.

Another aspect of the present invention is that the non-actuatable,wearable pad is formed of a material selected from the group comprisingalumina, TiC/A12O3 and silicon.

Another aspect of the present invention is that the non-actuatable,wearable pad is preferably less than 3.5% and more preferably less than2% and a preferred embodiment is 1%.

In another embodiment of the present invention, a method for forming aslider is provided. The method includes forming a slider body having afirst side, a second side, a leading edge and a trailing edge, using atleast a first etching to form an air bearing structure on the sliderbody extending to the trailing edge for providing a desired fly heightand using a last etching to form a non-actuatable, wearable pad on theair bearing structure extending to the trailing edge, the wearable padextending above the air bearing surface and having a surface area ofless than 5% of a total air bearing surface area and a predeterminedheight so that wearing of the pad during use produces an interference ofzero at the desired fly height and provides negligible lift to theslider.

These and various other advantages and features of novelty whichcharacterize the invention are pointed out with particularity in theclaims annexed hereto and form a part hereof. However, for a betterunderstanding of the invention, its advantages, and the objects obtainedby its use, reference should be made to the drawings which form afurther part hereof, and to accompanying descriptive matter, in whichthere are illustrated and described specific examples of an apparatus inaccordance with the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

Referring now to the drawings in which like reference numbers representcorresponding parts throughout:

FIG. 1 is a plan view of a disk drive;

FIG. 2 is a perspective view of an actuator assembly;

FIG. 3 illustrates a greatly enlarged view of a head gimbal assembly;

FIG. 4 shows a self-limiting wear contact pad slider according to thepresent invention;

FIG. 5 illustrates a side view of the slider of FIG. 4;

FIG. 6 illustrates the determination of the height of the protrudingelement surrounding the transducer;

FIG. 7 illustrates the burnish time versus the change in magnetic signalfor a slider according to the present invention;

FIG. 8 illustrates the burnish time versus the increase inelement-to-disk spacing;

FIGS. 9 a–b illustrate the effect of crown on fly heights; and

FIGS. 10 a–b illustrate the self-limiting characteristics of the contactpad slider according to the present invention.

DETAILED DESCRIPTION OF THE INVENTION

In the following description of the exemplary embodiment, reference ismade to the accompanying drawings which form a part hereof, and in whichis shown by way of illustration the specific embodiment in which theinvention may be practiced. It is to be understood that otherembodiments may be utilized as structural changes may be made withoutdeparting from the scope of the present invention.

The present invention provides a self-limiting wear contact pad sliderand method for making the same. A protruding element surrounding thetransducer is fabricated using a third etch step so that the protrudingelement has a height that is greater than or equal to the designed flyheight of the aerodynamic lift surface minus the disk roughness.

FIG. 1 is a plan view of a disk drive 100. Disk drive 100 includes adisk pack 112, which is mounted on a spindle motor (not shown) by a diskclamp 114. Disk pack 112, in one preferred embodiment, includes aplurality of individual disks which are mounted for co-rotation about acentral axis 115. Each disk surface on which data is stored has anassociated head gimbal assembly (HGA) 116 which is mounted to at leastone actuator assembly 118 in disk drive 100. An actuator assembly asshown in FIG. 1 is of the type known as a rotary moving coil actuatorand includes a voice coil motor (VCM) shown generally at 120. A voicecoil motor 120 rotates an actuator assembly 118 with its attached HGAs116 about a pivot axis 121 to position HGAs 116 over desired data trackson the associated disk surfaces, under the control of electroniccircuitry housed within disk drive 100.

More specifically, an actuator assembly 118 pivots about axis 121 torotate head gimbal assemblies 116 generally along an arc 119 whichcauses each head gimbal assembly 116 to be positioned over a desired oneof the tracks on the surfaces of disks in disk pack 112. HGAs 116 can bemoved from tracks lying on the innermost radius, to tracks lying on theoutermost radius of the disks. Each head gimbal assembly 116 has agimbal which resiliently supports a slider relative to a load beam sothat the slider can follow the topography of the disk. The slider, inturn, includes a transducer which is utilized for encoding fluxreversals on, and reading flux reversals from, the surface of the diskover which it is flying.

FIG. 2 is a perspective view of an actuator assembly 200. Actuatorassembly 200 includes base portion 222, a plurality of actuator arms226, a plurality of load beams 228, and a plurality of head gimbalassemblies 216. Base portion 222 includes a bore which is, in thepreferred embodiment, coupled for pivotal movement about axis 221.Actuator arms 226 extend from base portion 222 and are each coupled tothe first end of either one or two load beams 228. Load beams 228 eachhave a second end which is coupled to a head gimbal assembly 216.According to the present invention, multiple, independently controlledactuator assemblies 200 are provided in a disk drive.

FIG. 3 illustrates a greatly enlarged view of a head gimbal assembly300. Head gimbal assembly 300 includes gimbal 330, which has a pair ofstruts 332 and 334, and a gimbal bond tongue 336. Head gimbal assembly300 also includes slider 338 which has an upper surface 340 and a lower,air bearing surface 342. Transducers 344 are also preferably located ona leading edge of slider 338. The particular attachment between slider338 and gimbal 330 is accomplished in any desired manner. For example, acompliant sheer layer may be coupled between the upper surface 340 ofslider 338 and a lower surface of gimbal bond tongue 336, with anadhesive. A compliant sheer layer permits relative lateral motionbetween slider 338 and gimbal bond tongue 336. Also, gimbal bond tongue336 preferably terminates at a trailing edge of slider 338 with amounting tab 346 which provides a surface at which slider 338 isattached to gimbal bond tongue 336.

A conventional slider design starts off with a flat polished surface,from which a patterned air bearing surface (ABS) is created by a removalprocess such as etching or ion milling. The ABS surface is always thetop most polished surface and pressurizes with positive pressure to liftthe ABS up producing an air cushion above the disk. Air bearing surfacesare formed by single or dual etch processing which result in either 2 or3 surface levels, respectively.

FIG. 4 shows a self-limiting wear contact pad slider 400 according tothe present invention. The slider 400 is formed using a dual etch designwith three surface levels 410–416, wherein a third etch is added toproduce a fourth surface level 420. Accordingly, the top most surface isnow a small, non-actuatable wearable contact pad 420 around the magneticelement pole tips 422. The self-limiting contact pad 420 is wearable inthe sense that it is not formed of a hard overcoat that prevents wear,but rather exhibits wear when it comes into contact with the disksurface. This protruding pad 420 is small enough that it does not carryany significant amount of load and thus provides negligible lift to theslider due to its small size. This pad 420 is also small enough so thatit will wear quickly and easily and will not affect the fly height as itwears down, which provides the pad 420 with the ability to achieve aninterference of zero. The slider is simple to construct and isnon-actuatable. The slider comprises one or more materials selected fromalumina, TiC/AI₂O₃, or silicon. In addition to the rear pad 420, frontpads 416 are formed on side rails 418. The air bearing surfaces of thewear pad 420 is less than 5% of the total air bearing surface area, andis preferably less than 3.5% and more preferably less than 2%. In fact,a preferred embodiment is 1%.

FIG. 5 illustrates a side view 500 of the slider of FIG. 4. In FIG. 5,the four levels provided by the three etch steps are clearly evident.The front air bearing surfaces 510 includes three levels 512–516 thatare formed using the first two etch steps. The rear air bearing surfaces530 also include three levels 540–514. The protruding element 550surrounding the transducer 552 is fabricated using a third etch step sothat the protruding element 550 has a height that is greater than orequal to the designed fly height of the aerodynamic lift surface minusthe disk roughness.

The air bearing surfaces 516, 544, which pressurize and carry the loadof the slider 500, is now the second highest surface created by thethird etching process. The depth of the third etch produces anon-actuatable protruding pad 550 that is designed to be greater than orequal to the designed fly height of the original ABS surface prior toreceiving this third etch.

FIG. 6 illustrates the determination of the height of the protrudingelement surrounding the transducer. The air bearing surfaces of theslider are selected to provide a fly height of “M”. The roughness of thedisk surfaces is “N”. The difference between the fly height “M” and thedisk surface roughness “N” is calculated to be “X”. Thus, the protrudingelement surrounding the transducer is fabricated using a third etch stepso that the protruding element has a height “L” that is greater than orequal to the designed fly height of the aerodynamic lift surface minusthe disk roughness.

The slider thus flies at a certain fly height “M” and has a protrudingpad of “L” height which will put it in contact with the disk for a widerange of manufacturing tolerances. When the slider and disk are firstput together, the pad will interfere with the disk and will wear downuntil the interference is zero, at which point, the wear will be selflimiting and not continue further. This is because the air bearingsurface continues to support and lift the air bearing at its designedfly height.

Experiments have shown that this initial wear in process takes placefairly rapidly. FIG. 7 illustrates a graph 700 of the burnish time 710versus the change in magnetic signal 720 for a slider according to thepresent invention. FIG. 7 illustrates that the magnetic signal 730settles within about thirty minutes 740. FIG. 8 illustrates a graph 800the burnish time 810 versus the increase in element-to-disk spacing 820.FIG. 8 shows that the element-to-disk spacing 830 also settles in aboutthirty minutes 840. The end result of this design and burn-in processresults in a head/disk interface which is at contact or zerointerference and which can be reproduced on variety parts with a widerange of manufacturing tolerances.

FIGS. 9 a–b illustrate the effect of crown on fly heights. In order tobe able to adjust the flying height insitu in the disk drive, it isimportant to measure accurately the flying height in the disk drive.Methods for accurately measuring the flying height of the head in a diskdrive are disclosed in U.S. Pat. No. 4,777,544, issued Oct. 1, 1988 toBryon R. Brown et al. and assigned to International Business MachinesCorporation, which is hereby incorporated by reference. In Brown et al.,the amplitude of the magnetic signal at the nominal disk velocity iscompared to the amplitude at the touch down velocity of the slider-diskcombination using the Wallace spacing loss formula. In FIG. 9 a, theslider 900 doesn't touch the disk 910 at the location of the element912, but at the lowest point 920, which due the positive crown, is nearthe middle of the slider. The measured flying height (FH-M) 930 is lowerthan the actual spacing (FH-A) 932 between the magnetic element and thedisk, at the nominal disk velocity. This underestimate 940 of thespacing can be several tens of nanometers, making it virtuallyimpossible to determine spacings of 20 nm or less.

FIG. 9 b illustrates a second embodiment of a self-limiting wear contactpad slider 950 according to the present invention. In FIG. 9 b, theslider design solves this problem. If the height of the protruding pad960 is comparable to the nominal positive crown value, on decreasing thedisk velocity the slider 950 will touch the disk at a point on the pad960 and thus very close to the magnetic head. Knowing the pitch angle ofthe slider and geometry of the crown, one can select the pad height, sothat trailing end pad 960 touches the disk before other parts of theslider.

FIG. 10 a–b illustrate the self-limiting characteristics of the contactpad slider according to the present invention. The ABS design can beoptimized to maximize performance without regard to impact onsensitivities to manufacturing tolerances. FIG. 10 a illustrates theself-limiting wear contact pad slider with a first higher fly height1000. The protruding element 1010 contacts the surface of the disk 1012during burnishing. The first time the head flies on a 1014 disk, it isburnished by accessing across the disk several times. The protrusion1010 will wear down until the contact force is zero. After burnish 1020,the self-limiting wear contact pad slider exhibits a clearance 1030provided by the self-limiting wear characteristics of the protrudingelement.

FIG. 10 b illustrates the self-limiting wear contact pad slider with asecond lower fly height 1050. The protruding element 1060 still contactsthe surface of the disk during burnishing 1014. After burnish 1020, theself-limiting wear contact pad slider exhibits the same clearance 1030provided as exhibited in FIGS. 10 a. Thus, the self-limiting wearcontact pad 1060 decouples the ABS design and manufacturing tolerancesfrom contact force. The self-limiting wear contact pad slider improvesmagnetic performance by allowing the removal of recession and the carbonovercoat (COC). A tightly controlled spacing of a few nanometers can beachieved by applying additional wear.

The foregoing description of the exemplary embodiment of the inventionhas been presented for the purposes of illustration and description. Itis not intended to be exhaustive or to limit the invention to theprecise form disclosed. Many modifications and variations are possiblein light of the above teaching. It is intended that the scope of theinvention be limited not with this detailed description, but rather bythe claims appended hereto.

1. A method for forming a slider, comprising: forming a slider bodyhaving a first side, a second side, a leading edge and a trailing edge;using at least a first etching to form an air bearing structure on theslider body for providing a desired fly height, and using a last etchingto form a non-actuatable, wearable pad on the air bearing structure atthe trailing edge, the wearable pad being formed around a transducer andextending above the air bearing surface, the wearable pad having asurface area of less than 5% of a total air bearing surface area and apredetermined height selected to be greater than or equal to the desiredfly height minus a disk roughness, wherein the wearable pad erodesduring use to produce an interference of zero at the desired fly height.2. The method of claim 1 wherein the using at least a first etching toform an air bearing structure further comprises using two etching toform three surface levels.
 3. The method of claim 2 wherein the using alast etching to form a non-actuatable, wearable pad further comprisesforming a fourth surface level.
 4. The method of claim 1 furthercomprising forming at least one front air bearing pad.
 5. The method ofclaim 1 further comprising forming side rails extending along sides ofthe support structure.
 6. The method of claim 1 wherein thenon-actuatable, wearable pad is formed of a material selected from thegroup comprising alumina, TiC/AI₂O₃ and silicon.
 7. The method of claim1 wherein the non-actuatable, wearable pad comprises a surface area ofless than 3.5% of a total air bearing surface area.
 8. The method ofclaim 1 wherein the non-actuatable, wearable pad comprises a surfacearea of less than 2% of a total air bearing surface area.
 9. The methodof claim 1 wherein the non-actuatable, wearable pad comprises a surfacearea of 1% of a total air bearing surface area.